C4 - C1. Dominance occurs when one allele completely exerts...

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C1. Dominance occurs when one allele completely exerts its phenotypic effects over another allele. Incomplete dominance is a situation in which two alleles in the heterozygote have an intermediate phenotype. Codominance is when both alleles exert their effects independently in the heterozygote. And overdominance is a case in which the heterozygote has a phenotype that is superior to either homozygote. C2. Sex-influenced traits are influenced by the sex of the individual even though the gene that governs the trait may be autosomally inherited. Pattern baldness in people is an example. Sex-limited traits are an extreme example of sex influence. The expression of a sex-limited trait is limited to one sex. For example, colorful plumage in certain species of birds is limited to the male sex. Sex-linked traits involve traits whose genes are found on the sex chromosomes. Examples in humans include hemophilia and color blindness. C3. The term gene interaction refers to the phenomenon that two or more different genes can have an impact on the same trait. This can occur, for example, if two genes encode enzymes in the same metabolic pathway. If the pathway is disrupted by a mutation in either of these two genes, the same net result may occur. C4. If the normal allele is dominant, it tells you that one copy of the gene produces a saturating amount of the protein encoded by the gene. Having twice as much of this protein, as in the normal homozygote, does not alter the phenotype. If the allele is incompletely dominant, this means that one copy of the normal allele is not saturating. C5. Recessive alleles are often loss-of-function alleles. It would generally be more likely for a recessive allele to eliminate a trait or function rather than create one. Therefore, the peach carries the dominant allele while the nectarine has a loss-of-function allele that prevents fuzz formation. The recessive allele is in a gene that is necessary for fuzz formation. C6. There would be a ratio of 1 normal : 2 star-eyed individuals. C7. The red and white seed packs should be from true-breeding (homozygous) strains. The pink pack should be seeds from a cross between white- and red-flowered plants. C8. The amount of protein produced from a single gene is not a saturating amount. Therefore, additional copies produce more of the protein, whose functional consequences can be increased.
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This note was uploaded on 04/07/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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C4 - C1. Dominance occurs when one allele completely exerts...

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